Eric Muller notified me on one peculiarity of the FIPS codes for the Thai provinces - unlike almost all other countries the codes are assigned in the alphabetical order of the romanized name.

I haven't been able to find any sources which give a rationale for the coding scheme used, from the original codes used in FIPS 10-3 it seems a geographical ordering was used. The codes start with Mae Hong Son (TH01) in the northwestern corner, then continue through the northern provinces, then the northeast, central, east and finally southern provinces, ending with Yala (TH-70) as the southernmost province. But then there are the codes 71 and 72 for Ubon Ratchathani and Yasothon out of the order, and Narathiwat being placed in between the northeastern and central provinces as TH31.

Also interesting is the fact that the province Mukdahan, which was created in 1982, was not included in the original codes, only with the change from revision 10-3 to 10-4 in 1997, together with the three other provinces created in 1992. As FIPS 10-3 dates from 1984, this change might not have propagated into the sources used for creation of these codes by then, and none of the minor changes of the 10-3 codes catched it.

As it was custom in the FIPS coding scheme, with the split of a entity both the new entity as well as the modified one both get new codes assigned. There the change to FIPS 10-4 had the following code changes

TH21

TH73

Nakhon Phanom

TH78

Mukdahan

TH45

TH74

Prachinburi

TH80

Sa Kaeo

TH71

TH75

Ubon Ratchathani

TH77

Amnat Charoen

TH19

TH76

Udon Thani

TH79

Nong Bua Lamphu

Now going into speculation mode, maybe the fact that Ubon Ratchathani and Yasothon were placed at the end derives from the fact these two were split in 1972. Maybe there was a code list predating these FIPS 10-3 codes where Ubon Ratchathani had the TH31, and to prevent a renumbering of all the following codes after the split the two were placed at the end, and Narathiwat instead moved into the hole. But only an insider of the committees responsible for maintaining the FIPS 10 codes could shed a light on this oddity. And sadly none of the older FIPS codes beyond the 10-3 are available online, the best I could find was a list of changes to the country codes from the statoids website. It's odd that Google Books or similar don't have these Public Domain texts scanned yet.

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Changwat, Amphoe, Tambon

Everything about the administrative subdivisions of Thailand - history, current news, facts hardly found in English, reviews of corresponding books, the Wikipedia coverage of these entities...

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